These are known in the prior art plain paper electrostatic copying machines in which a drum carries a surface coating of photoconductive material, such for example as selenium. In operation of such a machine the surface of the drum is moved successively past the charging station at which a corona applies a uniform electrostatic charge over the surface of the drum and then to an exposure station at which the charged surface is exposed to an image of the original to be copied. At this station, the surface of the drum over relatively light areas of the image to be copied loses its charge while retaining its charge in relatively darker areas of the original, thus to produce a latent electrostatic image of the original to be copied.
Following the exposure station, the surface is carried through a developer station at which the latent image is subjected to the action of the developer including toner particles which adhere to the charged areas of the image, thus to develop the image. As the surface carrying the developed image leaves the developer station, it moves past a point at which a length of copy material, such as ordinary paper to which the image is to be transferred is fed to the drum so as to be carried along with the drum beneath a transfer corona. This transfer corona causes the particles of toner to migrate from the surface of the photoconductor to the surface of the copy sheet.
After the image has thus been transferred to the length of copy material, it is necessary to remove the sheet from the surface of the photoconductor which may, for example, be on a drum. In one particular arrangement employed to pick off a copy sheet carrying a developed image in a machine of the type described above, a stationary flexible band conforming to the configuration of the drum over a portion of the circumference thereof from the location at which copy material is fed to the drum to a location beyond the transfer corona is mounted at the edge of the drum, so that a narrow strip of copy material extending along a side thereof moves over the stationary flexible band as the length of copy material moves under the transfer corona. At the point at which the copy material is to be removed from the surface of the drum, a struck up portion of the flexible strip moves a leading corner of the length of copy material away from the drum and into the nip between a turn roll and a rubber belt, a portion of the length of which extends around and into contact with the surface of the turn roll. The turn roll is driven in cooperation with the belt to carry the developed sheet away from the photoconductive drum toward conveyor rollers which deliver the sheet to the user of the machine. This pick-off arrangement is illustrated in and is more fully described in Ariyama U.S. Pat. No. 3,936,045, for "Sheet Stripping Device for Copying Apparatus".
After the photoconductive surface leaves the pick-off station described hereinabove, it next moves through a cleaning station at which a sponge roller in engagement with the surface of the drum is driven in such a direction that the engaging surface portions of the roller and the drum move in opposite directions. This sponge roller normally is wet with developer to facilitate the cleaning action and to prevent scratching of the drum surface by toner particles which remain on the roller when the developer dries.
While the machine described above functions satisfactorily in most instances, it incorporates a number of serious disadvantages. First, it will readily be apparent from the description of the pick-off system described hereinabove, that the copy sheet can have no image transferred thereto over the space along the edge thereof which rides over the flexible band extending through the transfer station. Thus, where the original carries information or printing in this area, it will not appear on the copy. Attempts to obviate this problem by minor modifications for directing the corner of the sheet into the nip between the turn roller and the belt without the use of a strip extending through the transfer station have not proved successful since any developed image in the strip which formerly was blank became smeared or dirtied.
Landa Application Ser. No. 850,216, filed Nov. 9, 1977, now abandoned and replaced by continuation application Ser. No. 060,537 filed July 25, 1979, now U.S. Pat. No. 4,269,504, shows a pick-off system which overcomes the defects of the pick-off system described hereinabove. More specifically, Landa discloses a clutch assembly including a first continuously rotating element and a second element including a finger disposed in closely spaced relationship to the outer surface of the first member and restrained against rotation with the first element by a follower resiliently urged into engagement with a cam on the first member. The clutch assembly is mounted with the mouth of the narrow space closely adjacent to the surface of the photoconductor at a location beyond the transfer station of the machine. Means is provided for guiding the leading edge of the sheet into the mouth of the opening so that the clutch elements move together against the action of the cam follower biasing means to carry the leading edge of the sheet into the nip between a pair of delivery rolls. At that point the cam and follower under the action of the follower biasing means coact to release the clutch and to restore the second clutch element to its initial position. The Landa application suggests a number of specific devices for guiding the leading edge of a sheet of paper from the surface of the photoconductor into the mouth of the space between the two clutch elements. First, the application discloses a shoe pivoted on the machine frame and resting on the photoconductor surface at a location at which it intercepts the leading edge of the sheet. Secondly, the application discloses means for forming a crimp in the sheet so that the leading edge automatically enters into the mouth. A third device suggested in the application is an air jet directed toward the surface so as to lift the leading edge off the surface and into the mouth of the clutch space. While it is possible to direct the leading edge of the sheet into the clutch mouth by any of the means set forth in the Landa application none of these means are as certain in operation as is desirable. That is, while any of the means will operate for a certain period of time without failure, the occasions on which they fail to operate, resulting in paper jams, are too frequent.